Acrylonitrile polymer composition stabilized with metal formaldehyde sulfoxylate, a weak acid, and an inorganic acid and method of making same



United States Patet ACRYLONITRILE POLYMER COMPOSITION STA- BILIZED WITH METAL FORMALDEHYDE SUL- FOXYLATE, A WEAK ACID, AND AN INOR- GANIC ACID AND METHOD OF MAKING SAME Richard R. Holmes, Bethesda, Md., and Lloyd T. Jenkins,

Decatur, Ala., assignors to The Chemstrand Corporation, Decatur, Ala., a corporation of Delaware No Drawing. Application May 23, 1956 Serial No. 586,661

20 Claims. (Cl. 260-326) This invention relates to the stabilization of acrylonitrile polymers and blends thereof. More particularly, it relates to the stabilization of acrylonitrile polymers and blends thereof which have a tendency to develop color upon standing or application of heat.

The term polymer, as employed in the instant description and claims, is intended to include homopolymers, copolymers, and blends thereof, said polymers containing at least 80 percent by weight of polymerized or copolymerized acrylonitrile in the polymer molecule.

Acrylonitrile polymers containing 80 percent or more of acrylonitrile are generally insoluble in the more common solvents. In those instances where suitable solvents have been found, in order to efiect solution, the application of heat is usually necessary. Where heat is employed to effect solutions, from which shaped articles are to be formed, a tan to dark brown color frequently develops in the solutions and therefore is carried over ,into the product formed therefrom. This color also develops in solutions upon standing for prolonged periods of time. i

The mechanism which causes color formation has not been definitely ascertained, although a variety of reasons therefor have been advanced. The presence of metal ions, such as iron, copper and manganese in the solutions may cause the color. The employment of amide compounds as solvents may result in formation of amines when heat is applied and cause color in the compositions. Impurities present in the solvents have also been cited as a cause. Whatever may be the reason for color formation, it results in compositions and products of undesirable standards and therefore, has been the source of concern, particularly in commercial operations where such types of polymers or copolymers are employed.

Accordingly, it is an object of the present invention to prevent undesirable color formation in acrylonitrile polymer compositions.

Another object is to minimize color formation when solutions of the acrylonitrile polymers are permitted to stand for a prolonged period of time or upon application of heat.

It is also an object of the invention to prevent color formation in acrylonitrile polymers at elevated temperatures.

A still further object of the invention is the production of solutions of acrylonitrile polymers and articles pro- .duced therefrom having improved color characteristics.

Other objects and advantages will be apparent from a consideration of the description of the invention which follows hereafter.

In general, the objects of the invention are accomplished by dissolving the polymer of acrylonitrile in .a suitable solvent therefor and preventing or minimizing color formation by the presence in the solution as an inhibiting agent, a combined reagent comprising an organic metal sulfoxylateyan acid which complexes with metallic ions Patented Mar. 17, 1959 general formula,

0 l R OM In in which R is an alkanol group containing 1 to 3 carbon atoms, an acyl group containing 1 to 3 carbon atoms oi an aryl group containing 6 to 8 carbon atoms, ,n is an integer from 1 to 2, and M is sodium, potassium, zinc, etc. Compounds illustrative of this class are sodium formaldehyde sulfoxylate, zinc formaldehyde sulfoxylate, potassium formaldehyde sulfoxylate, zinc acetaldehyde sulfoxylate, sodium acetaldehyde sulfoxylate, potassium acetaldehyde sulfoxylate, zinc propionaldehyde sul'foxylate, sodium propionaldehyde sulfoxylate, potassium propionaldehyde sulfoxylate, etc.

Among the acids which form a complexwith metallic ions such as the ferric and ferrous ions, etc. are sulfamic acid, phosphoric acid, oxalic acid, tartaric acid, citric acid, etc. Although it is Well known that these acids will complex with metallic ions, it appears that their ability to do so is greatly improved when they are used in a combination with certain other acids such as those having an ionization constant greater than 1X10" and specifically enumerated below.

Among the acids having an ionization constant greater than 1 l0- which may be employed in practising the instant invention are sulfuric acid, hydrochloric acid, nitric acid, etc.

Among the solvents which may be used in practising the instant invention are N,N-dimethylformamide, N,N dimethylacetamide, aqueous zinc chloride, sulfuric acid, aqueous nitric acid, aqueous sodium thiocyanate, ethylene carbonate, sulfolane, nitromethane, etc.

The components of the inhibiting agent may be employed in equal or unequal amounts, any one constituent being present in a range of from 98 to 1 percent in a three component system. The total amount of inhibiting agent may be employed in a range of about 0.3 to 15 percent, based on the total polymer weight. However, it is preferred that the inhibiting agent of the instant invention be present in a small amount compared to the amount of polymer dissolved. Thus, although the amount is not critical, it is preferred that the inhibiting agent be present in the amount of about 0.3 to 3.0 percent, based on the total weight of the polymer. The inhibiting agent may be added to the solvents before or after the polymer is dissolved therein. The inhibiting agent permits exposure to high temperatures for prolonged standing periods without the development of the objectionable color which usually results in such solutions. The compositions of the instant invention may be prepared in a varying temperature range. For example, the compositions of the instant invention may be prepared by mixing the polymer, a suitable solvent and the inhibiting agent at any term perature or heating the mixture to a temperatureup to the boiling point of the solvent.

The polymeric materials, which maybe employed in the practice of the present invention, are polyacrylonitrile, copolymers, including binary and ternary polymers containing at least percent by weight of acrylonitrile in the polymer molecule, or a blend comprising polyacrylonitrile or copolymers comprising acrylonitrile with from 2 to 20 percent of another polymeric material, the blend having an overall polymerized acrylonitrile content of at least 80 percent by weight. While the preferred polymers employed in the instant invention are Fm inc i'method 'solution;polymerization methods, or aqueous 'ernul sion procedures. are. iz

polymer is prepared in finely divided form for im- .mediate use in the fiberfabrication operations. The

t ese containirig' at least 80 percent of acrylonitrile, generally recognized as the fiber-forming acrylonitrile polymers, it will be understood that the invention is likewise applicable to polymers containing less than 80 percent acrylonitrile and the same stability is realized with the inhibiting agents defined herein. The acrylonit'rile polymers containing", less than 80 percent acrylonitrile are useful in forming films, coating compositions, molding operations, lacquers, etc., in all of which applications the alleviation of undesirable color is extremely important.

For example, the polymer may be a copolymer of from 80 to 98 percent acrylonitrile and from 2 to 20 percent of another monomer containing the C=C linkage and copolymerizable with V, acrylonitrile. iinic monomers include acrylic, alpha-chloroacrylic and methaci-ylic 'a cids; the acrylates, such as methylmethacrylate,,ethylmethacrylate, butylmethacrylate, methoxyji'n thy; meta ata bta-ehlor'eeth 'l methacrylate, and th correspond g esters of acrylic andalpha-chloroacrylic acids; yinyl chloride, vinyl fluoride, vinyl bromide, vinyliden chloride, 1 chlor'o;l bromo-ethylene; metha'crylonitrile; acrylamide and methacrylamide; alpha-chloroacrylamide, or monoalkyl substitution products thereof; methyl vinyl ketone; vinyl carboxylates, such as vinyl acetate, vinyl chloroacetate, vinyl propionate, and vinyl stearate; N-vinylimides, such as N-vinylphthalimide and N-vinylsuccinimide; methylene 'malonic esters; itaconic acid and itaconic ester; N-vinylcarbazole; vinyl furane; alkyl vinyl esters; vinyl sulfonic acid; ethylenejalpha, beta-dicarboxylic acids or their anhydrides or derivatives, such as diethylcitraconate, diethylmesaconate, styrene, vinyl naphlthalene; vinyl-substituted tertiary heterocyclic amines, such as the vinylpyridines and alkyl-substituted vinylpyridines, for example, 2-vinylpyridine, 4-vinylpyridine, 2-

'methyl-5-vinyl pyridine, etc.; l-vinylimidazole and alkylsubstituted l-vinylimidazoles, such as 2-, 4-, or S-methyl- 1'-vinylimidazole, and other C=C containing polymerizable materials.

The polymer may be a ternary interpolymer, for example, products obtained by the interpolymerization of a'crylonitrile and two or more of any of the monomers, other than acrylonitrile, enumerated above. More specifi cally, and preferably, the ternary polymer comprises acrylonitrile, methacrylonitrile and 2-vinylpyridine. The ter- 1 nary polymers preferably contain from 80 to 97 percent ,ofacrylonitrile, from 1 to 10 percent of a vinylpyridine or a'1;vinylimidazole,and from 1 to 18 percent of another substance, such as "methacrylonitrile or vinyl chloride.

, Th'epp olym'ermay 'alsobea blend of polyacrylonitrile or j o'f'avbinary'interpolymer of from 80 to 99 percent rylonit'rile and from 1 to ZO-percent of at least one r CZ:C containingsubstance with from 2 to 50 percentof the weight' of the blend of'a'copolymer of from 10to 7 percent of 'acrylonitrilea'nd from 30 to 90 percent :ofat'least one other C=C containing polymerizable monomerh Preferably, when the polymeric material compr ses a blend, it will be a blend of a copolymer of 90 to 98 percentacrylonitrile and from 2 to percent of another mon'o olefinic' monomer, such as vinyl acetate, which is not receptive to dyestulf, with a sufficient amount of a lcopolymenofQt'rom 10 to 70 percent of acrylonitrile and fromto 90 percent of a vinyl-substituted tertiary heterocyclic amine, such as 'vinylpyridine or l-vinylimidazole, :to give a dyeable'blend having an overall tertiary heterocyclic amine content of from 2 to- 10 pervinyl-substituted cent, based on the weight of the blend.

The polymers, useful in the practice of the present rization procedures, such as mass polymerization I However, the preferred prac- -suspension polymerization wherein the preferred suspension polymerization may utilize batch Suitable mono-oleention, may beprepared by any conventional poly- 4 procedures, wherein monomers are charged with an aqueous medium containing the necessary catalyst and dis persing agents. A more desirable method involves the semi-continuous procedurein which the polymerization reactor containing the aqueous medium is charged with the desired monomers and the continuous withdrawal of polymer may also be employed.

The polymerization is catalyzed by means of any watersoluble peroxy compound, for example the potassium, ammonium and other water-soluble salts of peroxy acids, sodium peroxide, hydrogen peroxide, sodium perborate, the sodium salts of other peroxy acids, and any other water-soluble compound containing a 'peroxy group (-OO). A wide variation in the quantity of peroxy compound is possible. For example, from 0.1 to 3.0 percent by weight of the polymerizable monomer may be used. The catalyst may be charged at the outset of the reaction, or it may be added continuously or in increments throughout the reaction for the purpose of maintaining a more uniform concentration of catalyst in the reaction mass. The latter method is preferred because it tends to make the resultant polymer more uniform in its chemical and physical properties.

Although the uniform distribution of the reactants throughout the reaction mass can be achieved by vigorous agitation, it is generally desirable 'to promote the uniform distribution of reagents by using inert wetting agents, or emulsion stabilizers. Suitable reagents for this purpose are the water-soluble salts of fatty acids, such as sodium oleate and potassium stea'rate, mixtures of watersoluble fatty acid salts, such as common soaps prepared by the saponification of animal and vegetable oils, the amino soaps, such as salts of tri'ethanolamine and dode- 'cylmethylamine, salts of rosin acids and mixtures thereof, the water-soluble salts of half estersof sulfuric acid and long chain aliphatic alcohol, sulfonated hydrocarbons, such as alkyl aryl 'sulfonates, and any other of a wide variety of wetting agents, which are in general organic compounds containing both hydrophobic and hydrophilic radicals. The quantity of emulsifying agents will depend upon the particular agents selected, the ratio of monomer to be used, and the conditions ofpolymerization. Ingeneral, however, from 0.01 to 1.0 percentby weight of the monomers may be employed.

The emulsion polymerizations are'preferably conducted in glass or glass-lined vessels which are provided with a means for agitating the contents. Generally rotary stirring devices are the most effective means of insuring the intimate contact of the reagents, but other methods 'may be successfully employed, for example by rocking or tumbling the reactors. The polymerization equipment generally used lis conventional in the artand the adaptation 'ofa particular type of "apparatus to'th'e reaction contemplated is within thepr ovince "of one skilledin the art.

EXAMPLE I 7.5 grams of a polymerblend of-.88 percent ofua copolymer containing 94percent of acrylonitrile-randx'o percent of vinyl acetate and 12 percent of'a:copolynier of 50 percent of acrylonitrile and50 percentiof"2+meithyl- 5'-vinyl. pyridine were added to 45 milliliters fof.:N,-N- dimethylacetamide containing approximately 0.05 ,t-g'ram of titanium dioxide. The mixture was stirred and heated to 70 C. It was then quickly cooled to room temperature and the color measured. This sample was'used as a control. The purity is set forth below. :Subsequently,'like "samples wereprepared but with 0.225 ,gram: of ar'color inhibitor-containing 0.075; grame'achof-sodium: formaldeasraaoe Inhibitor Percentage Purity Used j Control Sodium Formaldehyde SulIoxylataSulfamic Acid and Sulfuric Acid 3 Sodium Formaldehyde Sulfoxylate, Phosphoric Acid and Sulfuric Acid EXAMPLE II 7.5 grams of a copolymer containing 94 percent of acrylonitrile and 6 percent of vinyl acetate were added to 45 milliliters of N,N-dimethylacetamide containing approximately 0.05 gram of titanium dioxide. The mixture was stirred and heated for 35 minutes at70 C. It was then quickly cooled to room temperature and the color measured. This sample was used as a control. The purity is set forth below. Subsequently, like samples were prepared but with 0.225 gram of a color inhibitor containing 0.075 gram each of sodium formaldehyde sulfoxylate, sulfamic acid and sulfuric acid; and sodium formaldehyde sulfoxylate, phosphoric acid and sulfuric acid. The purity is set forth below.

Table II Inhibitor Percentage Purity Used Control Sodium Formaldehyde Sulfoxylate, sulfamic Acid and Sulfuric Acid Sodium Formaldehyde Sulfoxylate, Phosphoric Acid and Sulfuric Acid EXAMPLE III sodium formaldehyde sulfoxylate, sulfamic acid and sulfuric acidyand sodium formaldehyde sulfoxylate, phosphoric acid and sulfuric acid. The purity is set forth below.

Table III Inhibitor Percentage Purity Used phoric Acid and Sulfuric Acid 3 The tests for color indicative of approaching whiteness used throughout the examples consist of measurements of purity as calculated from the tristimulus values determined on a General Electric Spectrophotometer by the methods recommended by the Standard Observer and Coordinate System of the International Commission on Illumination, as fully set forth in the Handbook of Colorimetry published by The Technology Press, Massachusetts Institute of Technology in 1936.

The compositions of the instant invention present many advantages. For example, products formed from the polymer solutions of the instant invention are free of objectionable color and therefore of greater commercial value. In preparing the polymer solutions, heat may be applied without the danger of color formation and the solutions, if necessary, may stand for prolonged periods and remain free of color. The inhibiting agentsare readily available and inexpensive. Therefore, no great increase in production cost is necessary. The compositions containing the inhibitors may be prepared without going through detailed and elaborate procedures that necessitate expensive changes in the design of the apparatus used to manufacture them.

It will be understood to those skilled in the art that many apparently widely different embodiments of this invention can be made without departing from the spirit and scope thereof. Accordingly, it is to be understood that this invention is not to be limited to the. specific and up to 20 percent of another polymerizable monoolefinic monomer copolymerizable therewith, a solvent therefor, and an inhibiting agent comprising substantially equal proportions by weight of a compound having the general formula,

wherein R is an alkanol group containing 1 to 3 carbon atoms and having the free valence on a carbon atom joined to the hydroxy group, n is an integer from 1 to 2, and M is a metal selected from the group consisting of sodium, potassium and zinc; an acid selected from the group consisting of sulfamic acid, phosphoric acid, oxalic acid, tartaric acid and citric acid; and an inorganic acid having an ionization constant greater than 1x10 2. A new composition of matter as defined in claim 1 wherein the polymer is a copolymer containing from to 98 percent of acrylonitrile and from 2 to 20 percent of another polymerizable mono-olefinic monomer co: polymerizable therewith.

3. A new composition of matter as defined in claim 1 wherein the polymer is a blend of 80 to .99 percent of (A) a copolymer containing to 98 percent of acrylonitrile and 2 to 10 percent of vinyl acetate and 1 to 20 percent of (B) a copolymer containing 10 to .70 percent of acrylonitrile and 30 to 90 percent of 2-methy1-5-vinyl pyridine.

4. A new composition of matter as defined in claim 1 wherein the polymer is polyacrylonitrile.

5. A new composition of matter as defined in claim 1 wherein the compound is sodium formaldehyde sulfoxylate.

6. A new composition of matter as defined in claim 1 wherein the compound is potassium formaldehyde sulfoxylate.

7. A new composition of matter as defined in claim 1 wherein the compound is zinc formaldehyde sulfoxylate.

8. A new composition of matter as defined in claim 1 wherein the acid is sulfamic acid.

9. A new composition of matter as defined in claim 1 wherein the acid is phosphoric acid.

10. A new composition of matter as defined in claim 1 wherein the acid is oxalic acid.

11. A new composition of matter as defined in claim 1 wherein the acid is tartaric acid.

12. A new composition of matter as defined in claim 1 wherein the acid is citric acid.

13. A new composition of matter as defined in claim 1 wherein the solvent is N,N-dimethylacetamide.

14. A new composition of matter comprising a copolymer containing 80 to 98 percent of acrylonitrile andmer, of an inhibiting. agent, said inhibiting agent comprising substantially equal proportions by weight of a compound having, the general formula,

i R 0 M wherein R is an alkanol group containing 1 to 3 carbon atoms. and. having the free valence on. a carbon atom joined. to the hydroxy group, n is an integer from 1. to 2,

and M is a metal selected from the. group consisting of sodium, potassium and zinc; an acid selected from the group consisting of sulfamic acid, phosphoric acid, oxalic acid, tartaric acid and citric. acid; and an inorganic acid having. an ionization constantv greater than 1 10- A new composition of matter comprising a polymer blend of 80 to 99 percent of (A) a copolymer containing 90 to 98 percent of acrylonitrile and 2 to 10 percent of vinyl acetate and 1 to percent of (B) a copolymer containing 10 to 70 percent of acrylonitrile and to 90 percent of Z-methyl-S-vinyl pyridine, a solvent therefor, and 0.3 to 15 percent, based on the total. weight of the polymer, of an inhibiting agent, said inhibiting agent comprising substantially equal proportions by weight of a compound having the general formula,

wherein R is an alkanol group containing 1 to 3 carbon atoms and having the free valence on a carbon atom joined to the hydroxy group, n is an integer from 1 to 2, and M is a metal selected from the group consisting of sodium, potassium and zinc; an acid selected from the group consisting of sulfarnic acid, phosphoric acid, oxalic acid, tartaric acid and citric acid; and an inorganic acid having an ionization constant greater than 1x10 16. A method for preparing a new composition of matter comprising mixing a polymer containing at least 80 percent of polymerized acrylonitrile and up to 20 percent of another polymerizable.mono-olefinic monomer copolymerizable therewith, a solvent therefor, and an inhibiting agent comprising. substantially equal. proportions by weight of av compound having the general formula,

R OJ M wherein R is an alkanol group containing 1 to 3 carbon atoms and having the free valence on a carbon atom joined to the hydroxy group, n is an integer from 1 to 2, and M' is a metal selected from the group consisting of sodium, potassium and zinc; an acid selected fromthe group consisting of sulfarnic acid, phosphoric acid, oxalic acid, tartaric acid and citric acid; and an inorganic acid having an ionization constant greater than l 10- and heating the mixture to form a homogeneous solution.

17. The method as defined in claim 16. wherein the polymer is a copolymer containing'from 80. to. 98. percent of acrylonitrile and from 2 to 20 percent. of another polymerizable mono-olefinic monomer copolymerizable therewith.

18. The method as defined in claim 16 wherein the polymer is a blend of 80 to 99 percent of (A) a copolymer containing 90 to 98 percent of acrylonitrile and 2 to 10 percent of vinyl acetate and 1 to 20 percent of (B) a copolymer containing 10 to percent of acrylonitrile and 30 to 90 percent of 2-methyl-5-vinyl pyridine.

19. The method as defined in claim 16. wherein the polymer is polyacrylonitrile.

20. A method for preparing a new composition of matter comprising mixing a polymer blend of to 99 percent of (A) a copolymer containing to 98 percent of acrylonitrile and 2 to 10 percent of vinyl acetatev and 1 to 20 percent of (B) a copolymer containing 10 to 70 percent of acrylonitrile and 30 to 90 percent of 2-methyl- S-vinyl pyridine, a solvent therefor, and 0.3 to 15 percent, based on the total weight of the polymer, of an inhibiting agent said inhibiting agent containing substantially equal proportions by weight of sodium formaldehyde sulfoxylate, sulfamic acid and sulfuric acid, and heating the mixture to a temperature in a range of 25 C. to the boiling point of said mixture to form a homogeneous solution.

References Cited in the file of this patent v 

1. A NEW COMPOSITION OF MATTER COMPRISING A POLYMER CONTAINING AT LEAST 80 PERCENT OF POLYMERIZED ACRYLONITRILE AND UP TO 20 PERCENT OF ANOTHER POLYMERIZABLE MONOOLEFINIC MONOMER COPOLYMERIZABLE THEREWITH, A SOLVENT THEREFOR, AND AN INHIBITING AGENT COMPRISING SUBSTANTIALLY EQUAL PROPORTIONS BY WEIGHT OF A COMPOUND HAVING THE GENERAL FORMULA, 